The following systems are conventionally known as examples of a system for opening and closing a sliding door or a back door of a vehicle: a system in which a portable device transmits a control signal to a vehicle when a user operates the portable device, and the door opens or closes according to the control signal; and a system in which the door opens or closes according to communication between a portable device and a vehicle when a user carrying the portable device approaches the vehicle (for example, see JP 2009-127336 A, JP 2014-227717 A).
JP 2009-127336 A discloses that, in a case where a user carrying the portable device approaches the vehicle, the timing of opening the door is made earlier when approaching speed is faster, and the timing of opening the door is delayed when the approaching speed is slower. Thus, the door is opened at a timing according to the approaching speed of the user to the vehicle. In addition, JP 2014-227717 A discloses that, time taken for the user to arrive at the vehicle is periodically calculated based on the distance from the portable device carried by the user to the vehicle and a temporal change in the position of the portable device, and opening speed of the door is controlled according to the time taken for the user to arrive at the vehicle.
In addition, a door opening and closing system is known which is capable of opening a door of a vehicle by a leg motion (for example, a kicking motion) even in a case where a user holds baggage with both hands (for example, see JP 2014-500414 W).
JP 2014-500414 W discloses that two sensors for detecting a kicking motion of a leg are disposed at different places at a rear of the vehicle. A time difference between a signal output from one sensor and a signal output from the other sensor is detected. In a case where the time difference satisfies a predetermined criterion, it is determined that a kicking motion of a leg is performed and the door is opened.
In a case of detecting a kicking motion of a leg and opening or closing the door of the vehicle, kicking speed varies from individual to individual. In the case of a user with faster kicking speed, the time from swinging forward of the leg to landing is shorter. In the case of a user with slower kicking speed, the time from swinging forward of the leg to landing is longer. In contrast, a door opening or closing operation is started after a fixed time has elapsed from a time point when sensor output is lowered to a predetermined level, in a process until the leg has landed (to be described later).
Therefore, if the kicking speed is faster, opening or closing of the door does not start at the time point when the leg has landed, and opening or closing of the door starts after a while. Therefore, the user feels that the time until the door has opened or closed is long. In contrast, if the kicking speed is slower, opening or closing of the door starts before the leg has landed. Therefore, the user feels that the time until the door has opened or closed is long.